Obesity has become a serious public health problem in both industrialized and rapidly industrializing countries. It increases greenhouse gas emissions through higher fuel needs for transportation of heavier people, lifecycle emissions from additional food production and methane emissions from higher amounts of organic waste. A reduction of average weight by 5 kg could reduce OECD transport CO2 emissions by more than 10 million t, while a reduction of consumption of energy-rich food to 1990 levels would lead to life-cycle emissions savings of more than 100 million t CO2 equivalent and by more than 2 million t through reduction of associated food waste. Due to the intimate behavioural nature of the obesity problem, policies to reduce obesity such as food taxation, subsidization of human-powered transport, incentives to reduce sedentary leisure and regulation of fat in foodstuffs have not yet been implemented to any extent. The emissions benefits of fiscal and regulatory measures to reduce obesity could accelerate the tipping point where a majority of voters feels that the problem warrants policy action.